Teknik Antarmuka Komputer #3 Antarmuka Komunikasi Serial

Transkripsi

1 Teknik Antarmuka Komputer #3 Antarmuka Komunikasi Serial Eka Maulana, ST, MEng. 1

2 Tujuan Kuliah Setelah mengikuti perkuliahan ini, mahasiswa dapat: 1. Memahami pertimbangan pemilihan jenis komunikasi serial 2. Menjelaskan mekanisme pengiriman data secara serial 3. Mengetahui jenis-jenis protokol komunikasi serial 4. Memahami antarmuka komunikasi serial 5. Merancang dan menganalisis teknik antarmuka serial 2

3 Outline Materi Pertimbangan Sistem Komunikasi Serial Parameter Komunikasi Serial Jenis Komunikasi Serial Komunikasi Asinkron/ Sinkron Teknik antarmuka serial Teknik pemrograman serial Aplikasi antarmuka serial Pengembangan antarmuka 3

4 Transmisi Paralel vs Serial Dua jenis komunikasi yang sering digunakan saat ini: Transmisi Paralel (Banyak jalur) 1. Data dikiring setiap satu pulsa clock (cepat) 2. Biasanya digunakan untuk jarak dekat: Serial Bulky mahal mahal (banyak jalur I/O). Rentan terhadap refleksi dan dapat terinduksi oleh noise. Banyaknya devais I/O tidak memiliki data rate yang cukup tinggi untuk mendukung transfer data secara parallel. 1. Serial dengan pengiriman setiap bit (lambat) 2. Setiap bit memerlukan satu pulsa clock 3. Secara umum digunakan untuk jarak jauh 4. Murah 4

5 Antarmuka Paralel Jalur data memungkinkan satu arah atau dua arah Lebar bus data biasanya ukuran byte (8 data bit). Sebuah byte penuh data ditransfer pada masing R/W siklus clock cycle. Chip Select (CS) memungkinkan beberapa perangkan untuk berbagi bus. 5

6 Antarmuka Serial Satu bit data ditransfer setiap satu pulsa clock (lambat tapi fleksibel). Serial Asinkron dapat diimplementasikan dengan jalur data saja. Masing masing perangkat membangkitkan clock clock sendiri 2 (Baud Rate Generator). Jalur handshaking dapat digunakan untuk status sinyal devais. Antarmukan serial sinkron memiliki jalur clock tersendiri. Sinyal Clock dibangkitkan oleh devais master. 6

7 Tipical Stuktur Port I/O Serial Antarmuka sistem bus Clock System Read/Write Select XMIT RCV Out Shift Register Input Shift Register Clock Transmitter Serial Data Out Clock Receiver Serial Data In Port merupakan antarmuka bus dimana mikroprosesor mampu: 1. Mengirim perintah ke port. 2. Membaca status port 3. Mengakses register data input/output port. Bus Data Interrupt Request Control Status Register Apa yang membedakan port ini dari struktur umum port I/O adalah konversi yang terjadi pada aliran (stream) data serial dan paralel. 7

8 Mekanisme I/O Serial Serial Communication Link Transmitter Receiver Transmitter mengencode sinyal data data untuk dikirim ke receiver. Timing sinyal data disasarkan pada clock f T transmitter Receiver mencuplik sinyal serial signal untuk mendecode data. Timing receiver sampling didasarkan pada clock f R receiver Untuk menangkap setiap bit data, timing sampling receiver harus disinkronisasikan terhadap sinyal yang dikirim oleh transmitter. Berdasarkan Teknik Sinkronisasi: (a) Sinkron (b) Asinkron 8

9 Sub Sistem Serial MCU memiliki dua sub system untuk antarmuka serial I. Protokol komunikasi serial Asinkron : Serial communication interface (SCI) dapat digunakan untuk menghubungkan terminal atau PC ke mikrokontroler. II. Protokol Komunikasi Serial Sinkron: Serial Peripheral Interface (SPI) dapat menyediakan komunikasi serial kecepatan tinggi terhadap perangkat atau to peripherals or other microcontroller units unit microcontroller lain. Sistem ini diperkenalkan oleh Motorola untuk memfasilitasi mekanisme pengiriman data antara mikrokontroler dengan devais lain. Protokol Sejenis: I 2 C (Philips), Micro-wire (National Semi) 9

10 Komunikasi Serial Asinkron Pada Komunikasi Asinkron, transmitter dan receiver Tidak menggunakan clock bersama Add: Start, Stop, Parity Bits Remove: Start, Stop, Parity Bits Transmitter + Data Receiver 1 byte-wide Data 1 byte-wide Data Transmitter Receiver Menggesert data data parallel ke jalur serial menggunakan clock-nya sendiri (internal) Menambahkan start, stop dan bit cek paritas Mengekstrak data menggunakan clock-nya sendiri (internal) Mengkonversi kembali data serial ke bentuk parallel setelah pemisahan start, stop dan bit paritas 10

11 Komunikasi Serial Asinkron Start bit menandai awal dari data word Stop menandai akhir dari data word Parity bit ditambahkan untuk deteksi kesalahan (opsional) Data bits data actual yang ditransmisikan Baud rate bit rate dari serial port (kecepatan transfer) Throughput data aktual yang ditransmisikan per detik (bit total yang ditransmisikan overhead) Contoh: baud = bits/sec Jika menggunakan 8-bit data, 1 start, 1 stop, dan tanpa bit paritas, throughput efektif: * 8 / 10 = bits/sec 11

12 Komunikasi Serial Asinkron Start Bit Parity Bit 1 or 2 Stop Bits D0 D1 D2 D3 D4 D5 D6 D7 1 Asynchronous Byte Transmisi asinkron mudah diimplementasikan namun memiliki efisiensi yang rendah mensyaratkan 2 hingga 3 bit tambahan untuk setiap data 8 bit. Metode ini biasanya digunakan untuk transmisi volume data yang kecil. 12

13 Komunikasi Serial Sinkron Transmitter Receiver CLK Sistem komunikasi sinkron selalu mengirim sinyal clock dengan data untuk mensinkronkan receiver untuk setiap waktu. Clock disediakan sebagai sinyal clock tersendiri atau dapat dipadukan dengan sinyal data itu sendiri. 13

14 Komunikasi Serial Sinkron Pada mode sinkron, transmitter dan receiver menggunakan clock bersama (sharing) Transmitter biasanya menyediakan sinyal clock tambahan yang terpisah dari data serial. Transmitter Clock Data Receiver 1 byte-wide Data 1 byte-wide Data Transmitter Menggeser data peralel menuju jalur serial menggunakan clocknya. Menyediakan clock sebagai sinyal terpisah Tanpa start, stop, atau bit paritas tambahan The Receiver Mengekstrak data menggunakan clock yang disediakan oleh transmitter Mengkonversi kembali data serial menjadi bentuk paralel. 14

15 Berdasarkan Mode Operasi Kanal Simplex Transmisi satu arah Biasanya disebut receive only transmission. Contoh: TV, Radio, PC Printer Half Duplex Full Duplex Transmisi dimungkinkan dua arah, namun tidak dalam waktu yang bersamaan. Komunikasi manusia adalah half-duplex. contoh: Beberapa komputer terhubung bersama-sama Full Duplex mengijinkan informasi (data) untuk ditranransfer secara simultan secara dua arah dalam waktu bersamaan. Contoh: Telephone Standard. 15

16 Konfigurasi Tradisional Host communicates with the terminals using a dedicated link. Terminals can communicate with each other via host only. Host communicates with the terminals using a shared connection. Terminals have to identify if data is intended to them (address) Other Topologies? Star, Mesh, Ring 16

17 Prinsip Kode Biner Serial Beberapa cara untuk identifikasi data (ex: menandai mark (1) dan spaces (0)). 1. NRZ 2. NRZI 3. RZ 4. CMI (Code Mark Inversion) 5. Manchester 6. Diff Manchester Teknik ini disebut dengan Tipe coding atau format modulasi. 17

18 Komunikasi Serial Sinkron Clock dapat disediakan terpisah atau dipadukan dengan data. Dua cara yang umum untuk memadukan clock ke dalam sinyal data dapat digunakan : (i) Manchester atau (ii) sinyal lebar pulsa variable. Catatan: Sinyal Berubah pada pertengahan setiap bit digunakan oleh receiver untuk sinkronisasi proses sampling. 18

19 Encoding Data Manchester 19 19

20 Serial Sinkron: Pemisahan sinyal Clock Other synchronous serial communication systems send the synchronization clock as a separate clock signal. The clock s rising edge always falls in the center of the data bit time. Examples: Motorola SPI, Phillips I 2 C, National MicroWire. The advantage of using a separate clock: 1. Circuit Simplicity (rising edge triggered shift register) 2. Data rate does not have to be fixed The disadvantage? 1. A Separate clock signal is required (long distance, expensive, reliability!) 20

21 Serial Komunikasi Asinkron Each device uses its own clock. The clocks must run at the same rate but do not need to be synchronized. The receiver clock must be within 4% of the transmitter clock. 21

22 UART : Universal Asynchronous Receiver Transmitter The UART is the interface chip that implements serial data transmission. Also known as (ACIA) asynchronous communication interface adapter. If you need more serial ports you would use an UART to interface with your MCU. Six major components: 1. Chip select & read/write cont 2. Data bus buffers 3. Transmit data Register 4. Receive data Register 5. Status Register 6. Control Register 22

23 Frame Data Asinkron Idle time The basic unit of information is the character or data frame A Frame is a complete and non divisible packet of bits. It includes both information (data) and overhead (extra bits) Synchronization is achieved using Start-Stop bits. i.e. the receiver needs to know when a character starts and when it stops => character is framed by start and stop bits 23

24 Start and Stop Framing. Parity The transmitter can send characters at any rate, so there may be delays between the transmission of each character The receiver detects the falling edge of the start bit and then attempts to sample in the center of each bit time. Parity is used to detect single bit errors type: even or odd the quantity of 1 bits in the data determine the parity bit The receiver also needs to know (i) number of data bits in each character, (ii) type of parity used if any, (iii) number of stop bits. 24

25 Start, Stop and Parity Bits 25

26 Contoh The letter `A is to be transmitted in the format with (i) 8 data bits (ii) no parity (iii) one stop bit Sketch the output The ASCII code for `A` is $41 or % LSB Idle Start Bit LSB MSB Stop Bit 26

27 Contoh: menggunakan RS V 0 V -15V Using RS-232 time Idle Start Bit LSB MSB Stop Bit 27 27

28 Contoh Show the framing bits when the char B (21) 16 is sent at 7 data bits, 2 stop bits, odd parity: Solution: 1. start bit: 0 2. data bits: parity bit: 1 4. stop bits:

29 Data Speed dan Baud Two units of speed are employed in data transmission. 1. # of data bits transmitted per second (BPS) 2. Baud : the rate at which the signal changes For a binary two-level signal, a data rate of one bit per second is equivalent to one Baud. if a data transmission system uses signals with 16 possible discrete level, each signal can have 16 = 2 4 different values (i.e., signal element encodes 4 bits) Example: If the 16-level signals are transmitted at 1,200 Baud, the data rate is 4 x 1,200 = 4,800 bps. Effective BPS = (nr of data bits)/(nr of frame bits) x baud 29

30 Contoh How long does it take to transmit one character at a speed of 9600 bauds? Each character is transmitted using a format of seven data bits, even parity, one stop bits. Solution: 1. Each character consists of 10 bits (1 start, 1 stop, 1 parity, 7 data) 1.Effective Data bit rate: 7/10 x 9600 = 6720 Bps 2. Each bit requires 104 us = (1/9600) 3. Thus each character will require : 10 x 104us = 1.04 ms 30

31 Standard RS-232 The RS-232 standard was established in 1960 by the Electronic Industry Association (EIA) for interfacing between a computer and a modem. The standard is referred to as either RS-232 or EIA-232 In data communication terms, both computers and terminals are called data terminal equipment (DTE). Modems and routers are called Data Communication Equipment (DCE) 31

32 Antarmukan Komunikasi Data 32

33 MODEM Modems is a contraction of modulator-demodulator Modem is used to send and receive serial digital data over a telephone line Basics of modems Modem is connected to a serial port dedicated circuit the serial port, the RS-232 data terminal equipment (DTE) -> connected to a modem, a data communication equipment (DCE) -> to a telephone line Transmission... Receiving... The audio signal is known as the carrier signal Tech: PSK; DPSK; QAM 33

34 Modulasi Carrier (Analog) 34

35 Modulasi Carrier (Digital) 35

36 Modulasi Fase Diferensial Phase is shifted by multiples of 90, therefore two bits at a time can be transmitted

37 The RS-232 Standard There are four aspects to the EIA-232 standard 1. Electrical specifications -- specifies the voltage level, data rates, distance of communication 2. Mechanical Specifications specify the number of pins and the shape and dimensions of the connectors. 3. Functional Specifications specify the function of each signal. 4. Procedural Specifications specifies the sequence of events for transmitting data 37

38 (1) The EIA-232 Electrical Specs The interface is rated at a signal rate less than 20 KBPS. With good design, however, we can achieve a higher data rate. The signal can transfer correctly within 15 meters. Greater distance can be achieved with good design. Driver maximum output voltage is -25V to +25V A voltage more negative than -3V at the receiver s input is interpreted as logic one. A voltage more positive than +3V at the receiver s input is interpreted as logic zero. 38

39 (2) The EIA-232 Mechanical Specs RJ45 (EIA-561) Connector V.24/RS-232 DB25 Pin Connector DB9 (EIA574) Connector 39

40 Mechanical: The EIA-232 Cable The simplest RS232 cable uses just : TXD, RXD and Ground with optional ground shield. The shield provides protection from electric field interference. 40

41 (3) Functional Specs I. DTR (Data Terminal Ready) (DTE) II. DSR (Data Set Ready) (DCE) III. RTS (Request to Send) (DTE) IV. CLS (Clear to Send) (DCE) V. RI (Ring Indicator) (DCE) VI. TX (Transmit) VII. RX (Receive) VIII.. 41

42 Cont Functional Specs 42

43 Procedural Specification E.g. Asynchronous private line modem (Point-to-Point Link ``Not over the phone line ) The modem will require only the following signals to operate: 1. GND, 2. Tx, Rx, 3. RTS, (Request to Send) 4. CTS, (Clear to Send) 5. DSR, (Data Set Ready) 6. DCD (Data Carrier Detect) Computer (DTE) Tx Rx DCD CTS RTS DSR GND Modem (DCE) Tx Rx DCD CTS RTS DSR GND Tx: transmit data Rx: receive data DCD: data carrier detect Direct link CTS: clear to send RTS: request to send DSR: data set ready Modem (DCE) Tx Rx DCD CTS RTS DSR GND Computer (DTE) Tx Rx DCD CTS RTS DSR GND Figure 9.2 Point-to-point asynchronous connection 43

44 (2) Functional/Procedural Specs I. DSR (Data Set Ready) From DCE (i.e., Modem is ready) II. RTS (Request to Send) DTE to DCE (i.e., DTE Wants to send info) III. CLS (Clear to Send) ACK from DCE (i.e., Data may be transmitted now) IV. Local Computer (i.e., DTE) sends data serially to modem. V. Local Modem (i.e., DCE) modulates signal but before that sends a carrier signal to remote modem. VI. Remote Modem detects the carrier signal ring and asserts DCD to inform remote DTE that a call arrived. VII. DCD (Data Carrier Detect) Remote Modem (i.e., DCE) indicates that a carrier frequency has been established. VIII. Remote Modem (i.e., DCE) receives modulated data, demodulates it and sends it to remote DTE. 44

45 Sequence of events occurred during data transmission over dedicated link 2. DTE asserts RTS 4. DTE starts to send data (to local DCE) Local 1. DCE asserts DSR 3. DCE asserts CTS Time Remote 5. DCE sends out a carrier and then the modulated data 6. DCE asserts DCD 8. DCE sends out demodulated received data 7. DTE waits for arrival of data 9. DEC receives demodulated data 45

46 Procedural Specification Over the telephone line the modems will have to go through the following phases: 1. Phase 1: Establishing the Connection 2. Phase 2: Data Transmission 3. Phase 3: Disconnection The modem will require more signals to operate: GND, Tx, Rx, RTS, CTS, DSR, DCD,.. Computer (DTE) Modem (DEC) Modem (DEC) Computer (DTE) Tx Rx RING DCD CTS RTS DSR DTR GND Tx Rx RING DCD CTS RTS DSR DTR GND Phone line Tx Rx RING DCD CTS RTS DSR DTR GND Tx Rx RING DCD CTS RTS DSR DTR GND Figure 9.3 Asynchronous connection over public phone line 46

47 Sequence of events occur during data transmission over public phone line Local (transmission side) time Remote (receiving side) Connection establishment phase 1. DTE asserts DTR 2. DCE dials the phone number 3. DCE detects the ring and asserts RING 4. DTE asserts DTR to accept the call 6. DCE asserts DSR and DCD and also sends out a carrier for full duplex operation 5. DCE sends out a carrier and asserts DSR 7. DCE asserts DCD (full duplex operation) 47

48 Sequence of events occur during data transmission (continued) Local (transmission side) time Remote (receiving side) Data transmission phase 1. DTE asserts RTS 2. DCE asserts CTS 3. DTE sends out data to DCE Disconnection phase 4. DCE modulates data and sends it out 5. DCE demodulates data and forwards the data to DTE 6. DTE receives data 1. DTE drops RTS 2. DCE drops CTS and drops the carrier 3. DCE deasserts DCD & DSR 4. DTE deasserts DTR 48

49 RS-232 Interface Standard: Summary Equipment using asynchronous serial com. normally use the RS-232 interface The logic levels used for RS- 232 signals are: +12 V for logic 0; -12 V for logic 1 This is to allow signals to be transmitted over greater distances This is a bipolar form of NRZ format The standard defines 25 different signals Many signals are not used => serial ports also use a DB-9 connector Common signals: Transmit data: TxD or TD Receive data: RxD or RD Request to send: TSR Clear to send: CTS Data set ready: DSR Signal ground: SG Data carrier detect: DCD Data terminal ready: DTR Ring indicator: RI From normal HCMOS and TTL levels we need to use special driver chips for... 49

50 Komunikasi Serial Sampai ketemu minggu berikutnya 50